Electroacoustical transducers are advantageous because they provide a conversion between electrical energy and acoustical energy. For example, when alternating current signals are introduced to an electroacoustical transducer, the transducer vibrates and produces acoustical energy in accordance with such vibrations. The conversion of electrical energy to acoustical energy has a number of different uses such as in loud speakers and in sonar applications, for example. Electroacoustical transducers have been known for a considerable number of years. One such transducer is described in U.S. Pat. No. 4,651,044 issued on Mar. 1, 1987 to Kompaneck.
U.S. Pat. No. 4,651,044 discloses an electroacoustical transducer generally illustrated at 10 and shown in prior art FIG. 1 including a tubular member 12 with a gap 14. The gap 14 has a relatively short circumferential length and extends axially along the full length of the member 12. The member 12 may be made from a metal such as a steel having elastic properties. The thickness and diameter of the metal tube are selected to produce vibrations, in the nature of the vibrations of a tuning fork, at a preselected frequency such as between approximately two (2) kilohertz and four hundred (400) hertz.
A plurality of sectionalized transducer elements 16 are arrayed within the member 12 in abutting and progressive relationship to one another and in abutting relationship to the inner wall of the member 12. The sectionalized elements 16 are provided with equal circumferential lengths and thicknesses and are disposed in symmetrical relationship to the member 12, and in symmetrical relationship to the gap 14 in the member. The sectionalized elements 16 are formed from a suitable ceramic material having piezoelectric characteristics. The elements 16 are bonded to the inner wall of the member 12 by a suitable adhesive 18. The adhesive 18 has properties for insulating the sectionalized elements from the tubular member 12. The ceramic material for the elements 16 and the adhesive 18 are well known in the art.
The sectionalized elements 16 are polarized circumferentially rather than through the wall thickness. Such a polarization is designated in the art as a “D33 mode”. Alternating current signals are introduced to the sectionalized elements 16 from a source 20. The introduction of such signals to the elements in the plurality may be provided on a series or parallel basis.
When alternating current signals are introduced from the source 20 to the elements 16, the signals produce vibrations of the sectionalized elements 16. These vibrations in turn produce vibrations in the tube 12, which functions in the manner of a tuning fork. The frequency of these vibrations is dependent somewhat upon the characteristics of the sectionalized elements such as the thickness and diameter of the tubular member or ring 12. As a result, for a ring 12 of a particular diameter, the resonant frequency of the transducer 10 may be primarily controlled by adjusting the thickness of the ring 12.
FIG. 2 illustrates another prior art transducer including a metal tube 12 corresponding to that shown in FIG. 1 and further including sectionalized elements 16. The sectionalized elements are linearly stacked in abutting relationship to one another and are attached to the inner wall of the tube 12 at diametrical positions equally spaced from the ends of the gap 14. The elements at the end of the stack are suitably bonded to the inner wall of the tubular member 12. Thus, when alternating current signals are introduced to the sectionalized elements, the elements vibrate and produce vibrations in the tube 12. The vibrations of the tube 12 at positions adjacent to the gap 14 in FIG. 2 are similar to the vibrations of the tube 12 adjacent to the gap 14 in FIG. 1.
In the prior art depicted in FIG. 3, a pair of driving rods 30 and 32 are connected to the ends of the tubular member 12 at a position adjacent the gap 14. Thus, the rods 30 and 32 move reciprocally in accordance with the vibrations of the tube 12. The rods 30 and 32 reciprocate in a push-pull relationship such that one of the rods is moving to the right at the same time that the other rod is moving to the left as the tube 12 expands and contracts. With high power, the rods 30 and 32 can work in such equipment as a pile driver or a trench digger. The frequency of the reciprocatory movement of the rods 30 and 32 can be approximately four hundred (400) hertz when the tubular member 12 has a diameter of at least one foot (1′0″) and a wall thickness of approximately five eights of an inch (⅝″) and has capabilities of being driven at a very high power such as a power of at least eight (8) kilowatts.
FIG. 4 shows the use of the transducer of FIG. 1 as a “remote” sonic system. Here the prior art transducer is coupled to a replaceable knife 40 through a flexible shaft 42. The use of the flexible shaft 42 provides the housing of the transducer and the source with a position displaced from an operator holding the knife 40. The flexible shaft 42 has a transverse modulus capable of propagating to the knife 40 the sound waves generated by the transducer. A system such as shown in FIG. 4 has a number of different applications including cutting, drilling and massaging.
FIG. 5 schematically illustrates the use of a plurality of the transducers of FIGS. 1 and 2 in an array having utility as a sonar transducer. The array is shown as being formed from six transducers. These transducers are respectively designated as 10a, 10b, 10c, 10d, 10e and 10f. The transducers in the array can be connected electrically in series or in parallel depending upon the pattern of the acoustical beam to be produced. The array can be encapsulated in a steel or rubber boot 50 which can be filled with oil 52. The transducers 10a through 10f are disposed with their gaps 14 in a particular phase relationship to one another in the annular direction. The gaps 14 for each of the successive transducers are shown as being rotated 90 degrees from the adjacent transducer. The acoustical power from the array can be directed in a beam having any directional properties desired by providing a proper phase relationship for the gaps in the different transducers. Such a phase relationship can be obtained by rotating the transducers so that their gaps face in particular directions relative to one another.
A plurality of transducers can also be mounted on a vertical rod 60 such as shown in FIG. 6. The length of this rod depends upon the area to be actuated acoustically. For example, eight transducers are shown in FIG. 6 as being mounted on the rod 60 in equally spaced relationship. Each of the transducers is shown as being rotated approximately 90 degrees from the transducer directly above it. This provides for an acoustical output having omnidirectional characteristics in the “near field” condition.
The above-mentioned prior art (e.g. FIGS. 1, 3 and 4) thus describe typical slotted cylinders driven with a cylindrical ceramic stack located on the inner diameter of the inert shell (FIG. 1). The prior art structure of FIG. 2 illustrates incorporation of a longitudinal driver to replace the more expensive and labor intensive ceramic cylinder stack. However, such an implementation of a longitudinal drive is likely to result in a broken stack due to bending moments imparted by the shell on the stack during operation. Further, such a structure results in poor electromechanical coupling due to stack bending and mismatching the very stiff stack to the low stiffness shell. Still further, the placement of the stack across the shell geometric center and halfway up the shell results in less than optimal motion amplification and the stack/shell interface would be subject to fretting corrosion. The wall driven stack (FIG. 1) is both expensive and prone to increased failure rates. Accordingly, alternative transducer driver designs are desired.